Add test.

tests/ImageSharp.Tests/Processing/Filters/BrightnessTest.cs

@@ -1,6 +1,7 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Processing.Processors.Filters;
 using Xunit;
@@ -26,5 +27,33 @@ namespace SixLabors.ImageSharp.Tests.Processing.Effects
 
             Assert.Equal(1.5F, processor.Amount);
         }
+
+        [Fact]
+        public void Brightness_scaled_vector()
+        {
+            var rgbImage = new Image<Rgb24>(Configuration.Default, 100, 100, new Rgb24(0, 0, 0));
+
+            rgbImage.Mutate(x => x.ApplyProcessor(new BrightnessProcessor(2)));
+
+            Assert.Equal(new Rgb24(0, 0, 0), rgbImage[0, 0]);
+
+            rgbImage = new Image<Rgb24>(Configuration.Default, 100, 100, new Rgb24(10, 10, 10));
+
+            rgbImage.Mutate(x => x.ApplyProcessor(new BrightnessProcessor(2)));
+
+            Assert.Equal(new Rgb24(20, 20, 20), rgbImage[0, 0]);
+
+            var halfSingleImage = new Image<HalfSingle>(Configuration.Default, 100, 100, new HalfSingle(-1));
+
+            halfSingleImage.Mutate(x => x.ApplyProcessor(new BrightnessProcessor(2)));
+
+            Assert.Equal(new HalfSingle(-1), halfSingleImage[0, 0]);
+
+            halfSingleImage = new Image<HalfSingle>(Configuration.Default, 100, 100, new HalfSingle(-0.5f));
+
+            halfSingleImage.Mutate(x => x.ApplyProcessor(new BrightnessProcessor(2)));
+
+            Assert.Equal(new HalfSingle(0), halfSingleImage[0, 0]);
+        }
     }
-}
+}